Mailing systems, such as, for example, a mailing machine, inserter, and the like, often include different modules that automate the processes of producing mail pieces. A typical mailing system includes a variety of different modules or sub-systems each of which performs a different task on the mail piece. The mail piece is conveyed downstream utilizing a transport mechanism, such as rollers or a belt, to each of the modules. In a mailing machine, such modules could include, for example, a singulating module, i.e., separating a stack of mail pieces such that the mail pieces are conveyed one at a time along the transport path, a moistening/sealing module, i.e., wetting and closing the glued flap of an envelope, a weighing module, and a metering/printing module, i.e., applying evidence of postage to the mail piece. In an inserter, such modules could include one or more feeders and collators, an envelope stuffing module, a moistening/sealing module, i.e., wetting and closing the glued flap of an envelope, a weighing module, and a metering/printing module, i.e., applying evidence of postage to the mail piece. The exact configuration of the mailing system is, of course, particular to the needs of the user.
Some high speed mailing systems may utilize more than one printing module in series. For example, some high speed inserter systems can process up to 22,000 mail pieces per hour. The printing modules in such high speed systems require maintenance at periodic intervals to clean the print heads, replace ink cartridges, etc. Such maintenance requires the print module to be inactive, i.e., not perform any print operations, for a certain period of time. In high speed systems, it would be required to stop the system completely to allow this maintenance period to occur. Because of the high volume of mail pieces processed, even very short periods of down-time for maintenance can significantly impact the throughput of the system. For example, halting a system that typically process 22,000 pieces per hour for only two minutes will reduce the throughput by 733 pieces per hour. If the maintenance is required to be performed at least once per hour, in an eight hour day the throughput of the machine will be decreased by almost 6,000 pieces. To minimize any down-time of the system, it is known to place two print heads or modules (collectively referred to hereinafter as print or printing modules) in series along the transport path, where only one of the printing modules is activated at a time. Thus, when one of the printing modules requires maintenance operations, it can be inactivated and the other printing module activated to print on the mail pieces. For example, if the first printing module requires maintenance, the first printing module is inactivated and the second printing module is activated. Mail pieces will pass through the first printing module, without being imprinted upon, to the second printing module, where printing will occur. When the second printing module requires maintenance, the second printing module is inactivated and the first printing module is activated. Mail pieces will be imprinted upon by the first printing module and will pass through the second printing module without being imprinted with any information.
Modern mailing systems utilize digital printing techniques for producing images on a mail piece. Conventional digital printing techniques include bubble jet and ink jet, each of which produces an image in a dot matrix pattern. With digital printing, individual print head elements (such as resistors or piezoelectric elements) are selectively electronically stimulated to expel drops of ink from a reservoir onto a substrate, e.g., a mail piece. In either case, by controlling the timing of energizing of the individual print head elements in conjunction with the relative movement between the print head and the mail piece, a dot matrix pattern is produced in the visual form of the desired image. In the case of mailing systems, the image may be, for example, an indicium that evidences payment of postage.
Digital printing technology has significant advantages when used in a mail handling apparatus as compared to older technology that utilized either a flat platen or a rotary drum to imprint information, such as, for example, address information or an indicium, on mail pieces. For example, if some variable image data needs to be changed, it can easily be done through the installation of new or upgraded software versus having to replace the entire printing module, since the flat platen and drum are typically not separately removable. Moreover, greater printing speeds can be obtained as compared to conventional mechanical printing systems. However, the use of a digital print head in a mailing system presents other issues that must be taken into consideration. For example, for the ink jet nozzles of an ink jet printer to properly deposit ink on the surface of the receiving medium, it is critical that a small predetermined gap be maintained between the exit plane of the nozzles and the surface of the receiving medium, typically in the order of one sixteenth to one thirty-second of an inch. This gap is necessary to achieve acceptable image quality, since too small a gap causes scuffing of the print head and to large a gap results in inaccurate dot placement, with either situation resulting in a deteriorated print image. Thus, in the mail handling environment, it becomes necessary to maintain this critical gap between the exit plane of the ink jet nozzles and the upper surface of the mail pieces being conveyed through the mailing machine.
To accomplish this, the mail pieces, such as, for example, envelopes, postcards, flats, and the like, must be conveyed with the front panels on which the information is printed lying in a fixed registration plane, which is disposed beneath the exit plane of the nozzles a distance equal to the aforementioned gap. This arrangement is referred to hereinafter as top registration. To accomplish this top registration, a biasing force is applied to the back panel of the mail piece such that the front panel maintains contact with a registration plate. An opening is provided in the registration plate, above which the print head is located such that the print head can print on the mail piece as it passes the opening in the registration plate.
There are problems, however, with the conventional top registration transports in mailing systems. For example, friction between the mail piece and registration plate results in the generation of paper dust. The presence of dust within a mailing system can cause several problems, including, for example, clogging the nozzles of the print head. Dust accumulation can also interfere with maintenance operations performed by the mailing system on the print head, including, for example, wiping and capping of the print head. Another problem with top registration is the potential for the trailing edge of a mail piece to hit the print head as it is transported past the print head, thereby potentially damaging the print head. Systems with multiple printing modules present additional problems with conventional top registration. For example, even though one of the printing modules is inactivated, i.e., not printing, the mail pieces still must pass through both print modules. Although printing is not occurring in one of the modules, the mail pieces are still transported through the inactive printing module in a top registration position. Thus, the front panel of the mail piece is still in contact with registration plate, resulting in the generation of additional paper dust. Having to pass each mail piece through two printing modules will double the amount of paper dust generated, thereby increasing the risk of associated problems. Another problem with multiple printing modules is the smearing of ink printed on a mail piece by the first print module as the mail piece passes through the second print module. There is insufficient time for the ink deposited on a mail piece by the first print module to dry before the mail piece reaches the second print module. As such, the wet ink can smear when the mail piece makes contact with the registration plate of the second print module. The smearing of the ink can result in unreadable information. This is especially critical in the case of an indicium that includes a bar code that must be scanned for verification purposes. If the bar code is unreadable, the indicium cannot be verified and the mail piece may not be delivered.
Thus, there exists a need for a top registration device for a mailing system that reduces the problems of dust generation, ink smearing, and contact of the print head by the trail end of a mail piece.